package com.lagou.sqlSession;

import com.lagou.config.BoundSql;
import com.lagou.pojo.Configuration;
import com.lagou.pojo.MappedStatement;
import com.lagou.utils.GenericTokenParser;
import com.lagou.utils.ParameterMapping;
import com.lagou.utils.ParameterMappingTokenHandler;

import java.beans.PropertyDescriptor;
import java.lang.reflect.Field;
import java.lang.reflect.Method;
import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.ResultSetMetaData;
import java.util.ArrayList;
import java.util.List;

/**
 * @author czq
 * @date 2020/6/21 0:49
 * @description
 */
public class SimpleExecutor implements Executor {

    @Override
    public <E> List<E> query(Configuration configuration, MappedStatement mappedStatement, Object... params) throws Exception {

        PreparedStatement preparedStatement = getPreparedStatement(configuration, mappedStatement, params);

        // 5.执行 sql
        ResultSet resultSet = preparedStatement.executeQuery();
        String resultType = mappedStatement.getResultType();
        Class<?> resultTypeClass = getClassType(resultType);
        ArrayList<Object> objects = new ArrayList<>();

        // 6.封装返回结果集
        while (resultSet.next()) {
            Object o = resultTypeClass.newInstance();
            // 元数据
            ResultSetMetaData metaData = resultSet.getMetaData();
            for (int i = 1; i <= metaData.getColumnCount(); i++) {
                // 字段名
                String columnName = metaData.getColumnName(i);
                // 字段的值
                Object value = resultSet.getObject(columnName);

                // 使用反射或者内省，根据数据库表和实体的对应关系，完成封装
                PropertyDescriptor propertyDescriptor = new PropertyDescriptor(columnName, resultTypeClass);
                Method writeMethod = propertyDescriptor.getWriteMethod();
                writeMethod.invoke(o, value);
            }
            objects.add(o);
        }

        return (List<E>) objects;
    }

    @Override
    public int update(Configuration configuration, MappedStatement mappedStatement, Object... params) throws Exception {
        PreparedStatement preparedStatement = getPreparedStatement(configuration, mappedStatement, params);
        return preparedStatement.executeUpdate();
    }

    private PreparedStatement getPreparedStatement(Configuration configuration, MappedStatement mappedStatement, Object... params) throws Exception {
        // 1.注册驱动，获取链接
        Connection connection = configuration.getDataSource().getConnection();

        // 2.获取 sql 语句：select * from user where id = #{id} and username = #{username}
        // 转换 sql 语句：select * from user where id = ? and username = ?，转换过程中，还需要对 #{} 里面的值进行解析存储
        String sql = mappedStatement.getSql();
        BoundSql boundSql = getBoundSql(sql);

        // 3.获取预处理对象：preparedStatement
        PreparedStatement preparedStatement = connection.prepareStatement(boundSql.getSqlText());

        // 4.设置参数
        // 获取到了参数的全路径
        String paramterType = mappedStatement.getParamterType();
        Class<?> paramtertypeClass = getClassType(paramterType);

        List<ParameterMapping> parameterMappingList = boundSql.getParameterMappingList();
        for (int i = 0; i < parameterMappingList.size(); i++) {
            ParameterMapping parameterMapping = parameterMappingList.get(i);
            String content = parameterMapping.getContent();

            // 反射
            Field declaredField = paramtertypeClass.getDeclaredField(content);
            // 暴力访问
            declaredField.setAccessible(true);
            Object o = declaredField.get(params[0]);

            preparedStatement.setObject(i + 1, o);
        }

        return preparedStatement;
    }

    private Class<?> getClassType(String paramterType) throws ClassNotFoundException {

        if (paramterType != null) {
            return Class.forName(paramterType);
        }

        return null;
    }

    /**
     * 完成对 #{} 的解析工作：1.将 #{} 使用 ? 进行代替。2.解析出 #{} 里面的值进行存储
     * @param sql
     * @return
     */
    private BoundSql getBoundSql(String sql) {

        // 标记处理类：配置标记解析器来完成对占位符的解析处理工作
        ParameterMappingTokenHandler parameterMappingTokenHandler = new ParameterMappingTokenHandler();
        GenericTokenParser genericTokenParser = new GenericTokenParser("#{", "}", parameterMappingTokenHandler);

        // 解析出来的 sql
        String parseSql = genericTokenParser.parse(sql);
        // #{} 里面解析出来的参数名称
        List<ParameterMapping> parameterMappings = parameterMappingTokenHandler.getParameterMappings();

        return new BoundSql(parseSql, parameterMappings);
    }
}
